The present invention relates to novel polyimide resins.
The cost and weight of aerospace structures can be significantly reduced by the application of high-performance polymeric composites. By replacing metallic components with composite materials, significant weight and cost savings between 25 and 30 percent can be realized. The advent of high modulus fibers and thermally stable polymers made it possible for the introduction of composites into 316° C. (600° F.) temperature regimes. To this end, researchers at NASA Lewis Research Center developed a high-temperature addition polyimide called PMR-15 (Polymerization of Monomeric Reactants, 1500 molecular weight), which, over several decades, became the high-temperature matrix resin “work horse” for the aerospace industry for composite applications in the range of 250° C. to 325° C. The reactant monomers for PMR-15 consist of the monomethyl ester of 5-norbornene 2,3-dicarboxylic acid (nadic ester, NE), the dimethyl ester of 3,3′,4,4′-benzophenonetetracarboxylic acid (BTDE), and 4,4′-methylenedianiline (MDA).
However, PMR-15 contains 4,4′-methylenedianiline (MDA), a known animal carcinogen, a suspected human carcinogen, and a known kidney and liver toxin. When quantities of PMR-15 prepreg are being manufactured, or when this material is being produced into composite structures, exposure to MDA becomes a serious health hazard.
Currently, researchers at NASA-Lewis have developed a polyimide resin called AMB-21 which replaces MDA with 2,2-bis(4-[4-aminopnenoxyl]phenyl)propane (BAPP), a non-toxic, non-carcinogenic monomer. AMB-21 has further benefit in that it may be formed into composite components by using resin transfer molding (RTM). RTM fabrication techniques fall into the category of “low-cost” composite processing, since RTM can cut the manufacturing costs by up to 50%. Unfortunately, AMB-21 has a glass transition temperature (after post-cure) of only 285° C., which also falls short of the PMR-15 goal to achieve a 316° C. composite use-temperature.
Accordingly, it is an object of the present invention to provide a novel polyimide resin which overcomes many of the disadvantages of known polyimide resins.
Other objects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.